It's optional for any content provider. It's not required but what's the big issue? Google has already said they pay for this type of service to other providers. If company's a willing to pay to reach more customers on limited plans, then let them.
FYI: when you make a claim (even one that is obviously correct), the burden is on the claimant to support his or her claim. The reader has no burden to do their work for them.
I would consider his comment to be common knowledge and courtesy as well as posting etiquette.
If you are going to make a claim then it is on your to provide the support to such claim. Otherwise, you can't really argue with someone that claims otherwise.